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TRAININING COURSE

ONBUILDING SERVICES

AIR CONDITIONING, HEATING AND VENTILATION

IN BUILDING (HVAC SERVICE)

Prepared by

Eng. M.H.M. Shafiqul Islam



1.1 Types of Air Conditioning plants

1. Definition of Air Conditioning: Air Conditioning is defined as the

simultaneous control of temperature, humidity, motion and quality of

atmosphere within an enclosed space.

The functions of air-conditioning system are:

1. Temperature control (cooling and heating).

2. Humidity control3. Air filtering and purification.

4. Air movement and circulation.

5. Noise level control.

Summer comfort condition for human:

Temperature range : 74 0F - 78 0F

Humidity range: 50% - 60%

Air movement : 15 fpm-25fpm

Types of Air Conditioning plants:

Air-conditioning systems are classified broadly into the following types:

1. Direct expansion system (DX)

2. Central air conditioning system

3. Heat pump.

1. Direct expansion system (DX):

It is a self-contained compact unit located within or next to the air

conditioned space and consists of minimum essential components for producing

cooling effect. This system may be subdivided:

i) Room air conditioning unit (window type).

ii) Split air conditioning unit.

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iii) Single package air conditioning unit.

i) Room air conditioner: A room air-condition can be described as a self-

contained unit either mounted in a window through a wall or as a console.

ii) Split air-conditioning unit: This system consists of two individual

factory assembled units called indoor and outdoor unit separated from

each other but connected together by piping.

iii) Single package air-conditioning unit: This type of unit has both the

condensing and evaporating units in one package. Duct system is required

for conveying the conditioned air from the evaporating unit to the space

being conditioned.The above type air conditioners are low in cooling capacity and suitable

for using in small aid medium size room.

2. Central air-conditioning system:

Central air-conditioning system is generally divided into three basic types

of the methods through which the final space cooling and heating are attained.

These are as follows:i) All-air system.

ii) All-water system.

iii) Air-water system.

i) All-air system: Both the air treating and refrigeration plants may be

remotely located in separate room from the conditioned space. Only the

final cooling-heating medium (air) is brought into the condition spacethrough duct networks and air outlets.

Secondary refrigerant (i.e. chilled water) is supplied to the air-handling

unit from the refrigeration unit located in a remote plant room.

ii) All-water system: A cooling medium (chilled water) is supplied from a

remote refrigeration unit and circulated through coils of air terminal unit

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(FCU) installed within the conditioned space.

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The unit must be grounded to prevent possible hazards due to insulation

failures.

Power supply should be within the rated voltage.

Operation of the central plant is somewhat different from self-contained

unit. A well-sequenced operation procedure should be maintained and

operation should be carried out through trained/skilled staffs as per operation

manual. Record and checklist card should be maintained for each machine.

Maintenance:

Preventive maintenance is used for air conditioning plants. It

prevents down time occurring due to failure.

A checklist is prepared for weekly, monthly, half-yearly and annual

checks.

The essential aims of proper maintenance are:

Cleanliness (Clean filler regularly)

Correct lubrication

Proper electrical protection and control.

Correct tightness and leakage free performance.

Proper function of safety devices.

Relevant BNBC/93 codes for installation, Operation, and maintenance

of air conditioning plants.

3.5.1.5 Equipment Installation

a) General: Mechanical equipment and appliances shall be installed in

accordance with the manufacturer’s installation instructions for the labelled

equipment. Connections to mechanical equipment or appliances such as fuel

supply, electrical, hydraulic piping, vent and ducts shall conform to the

requirements of this code.

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b) Clearance: Appliances shall be installed with the minimum clearances to

combustibles for which the appliance has been tested as specified by the

manufacturer.

c) Anchorage of Appliances: Appliances designed to be fixed in position

shall be securely fastened in position. Supports for appliances shall be

designed and constructed to sustain vertical and horizontal loads within

the stress limitations specified in the Building Code.

d) Noise and Vibration: Equipment noise and vibration transmitted to the

occupied space shall not exceed the recommended value for the space. Selection

and installation of equipment shall be in accordance with Sec. 3.3.3.d) Identification of Equipment: When more than one air-conditioning,

heating, refrigerating or ventilation systems are installed on the roof of a

building or within the building, each equipment shall be identified as to

the area or space served by the equipment.

3.10.2 Operation

A well sequenced operation procedure shall be followed to ensureeffective operation of the air-conditioning, heating and ventilation

system, safety from hazard to personnel and property. Operation

procedure shall take account for saving in energy use.

All operation data of all the machinery and equipment shall be properly

preserved for future reference for maintenance purposes.

3.10.3 MaintenanceA well designed maintenance program for the air-conditioning, heating and

ventilation system shall be implemented in order to achieve the following:

a) Optimum reliability and continuity of service.

b) Extended longevity and economic life.

c) Functional effectiveness, whereby the intended performance of

mechanical equipment and system can be fully attained.

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d) Minimum operating cost, attendant requirements, servicing and repairs.

e) Safety from hazard to personnel and property.

Maintenance program and procedure shall comply with the instructions of

machinery/equipment manufacturers in this regard.

1.2 Refrigeration Cycles

Fundamentals

For an understanding of refrigeration and air conditioning, it is necessary

to know some fundamentals, technical/scientific terms and definitions.

Temperature:Temperature is an indication of the level of heat in a substance. A

thermometer is the instrument used for the measurement of temperature. There

are three different types of temperature: dry-bulb, wet-bulb and dew-point.

Dry-bulb temperature is the temperature that measured by an ordinary

thermometer.

Wet-bulb temperature is a measurement used to evaluate the humidity of air.

Dew-point temperature is the temperature at which vapour (at 100% humidity)

begins to condense.

Heat: Heat is a form of energy that causes molecules to move and raises the

temperature of a substance. It is measured in BTU/Calorie.

One BTU is defined as the amount of heat to be added (removed) to raise

(lower) the temperature of one pound of water by one degree Fahrenheit (1 0F).

There are three types of heat in air-conditioning and refrigeration: specific heat,

sensible heat and latent heat.

Specific heat is the amount of heat in BTU to raise the temperature of 1 lb of a

substance by 1 0F.

Sensible heat: Heat that changes the temperature of a substance. It can be

sensed on a thermometer.

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Latent Heat: heat that causes a change of state of substance with no change in

temperature or pressure.

There are different types of latent heat in refrigeration system.

Latent heat of condensation: The amount of heat released by a substance to

change its state from a vapor (gas) to a liquid.

Latent heat of fusion: The amount of heat that must be added to a solid to

change it to a liquid.

Latent heat of vaporization: The amount of heat that must be required to a

substance to change it from a liquid to a vapor.

Pressure: Force per unit area measured on either the absolute or atmospheric(gauge) scale. PSIA (LB/sq. in absolute) is the total pressure. PSIG (LB/sq.

gauge) is the pressure compared to atmospheric pressure (14.7psi).

PSIA = PSIG+ Atmospheric pressure.

Saturation: a condition existing when a substance contains the largest quantity

of another substance it can hold for that temperature and pressure.

Condensation: the process whereby vapor changes to a liquid without changingtemperature due to removal of heat (latent) to the surroundings.

Evaporation/vaporization: is the process by which a liquid changes into vapor

by absorbing heat.

Relative humidity: The relationship of the actual humidity in the atmosphere to

the maximum that air could hold at that temperature and pressure.

Enthalpy: the total amount of thermal energy (heat) contained in a fluid. Thisdepends on the fluid nature, pressure and temperature.

Ton of refrigeration: the amount of cooling produced by melting 1 ton of ice

in 24 hours.

Refrigeration Cycle

If we take a liquid refrigerant, confine it in a container and place this

container near a warm object, the liquid will absorb heat from the warm

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object. If enough heat is absorbed by the liquid refrigerant, it will boil and

vaporize. If the vaporized refrigerant gas is sufficiently compressed, it

will give up the heat that absorbed from the warm object, and the gas will

condense back to a liquid. This process of at alternatively vaporizing and

condensing a refrigerant is called a refrigeration cycle. When the cycle is

accomplished continuously through the use of machinery, it is called

mechanical refrigeration and also called vapour compression cycle.

Vapour Compression Cycle:

The basic components required to make up a refrigeration system are:

1. An evaporator- the cooling coil

2. A pump -the compressor

3. A condenser - the heat disposer

4. A liquid metering device-expansion value or capillary tube.

Evaporator: The refrigeration component known as the cooling coil, chiller and low side of the system. The liquid enters the evaporator tubes or shell, its

pressure drops to the pressure inside the evaporator. The refrigerant passes

through the evaporator coil, it continues to absorb heat from the surrounding

area to be cooled and vaporize. The absorption of heat by the vaporizing

refrigerant produces the cooling.

The refrigerant vapour leaves the evaporator through the suction line and flowsinto the compressor. There it is compressed into a hot, high pressure gas.

The compressor inlet ends the low side of the system.

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Compressor: The compressor whose function is to draw the refrigerant vapour

from the evaporator suction line and compress it from a low-pressure, low-

temperature gas to a high-pressure, high temperature gas.

The compressor lowers the pressure in the evaporator, making it colder than

surrounding air or water. The refrigerant absorbs heat from the surrounding area

and vaporizes.

At the compressor outlet high-pressure, high temperature gas is discharged into

the condenser. The outlet starts the high side of the system.

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the conversion of the refrigerant vapour (coming from the evaporator)

into liquid. In the absorption system, the condenser is also used but

compressor is replaced by the combination of the absorber-generator.

The refrigerant used in the absorption system is one whose vapour is

highly soluble in the another liquid or solution called the absorbent. The

absorbent should be nonvolatile. Two containers, one containing the

refrigerant (evaporator) and the other containing the absorbent (absorber)

are interconnected. The refrigerant liquid vaporizes in the evaporator.

Because of the strong affinity of the absorbent for the refrigerant vapour,

the absorbent in the absorber absorbs the vapour formed in the

evaporator, there by reducing the vapour pressure in the evaporator and

allowing the refrigerant liquid to vaporize continuously in the evaporator

to produce refrigeration. The absorbent, which has sucked and dissolved

the refrigerant vapour is sent to the generator. In the generator the

solution (absorbent) is heated by means of hot water or a steam coil (tube

bundle). On getting heat, the solution releases (discharged) the refrigerant

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vapour which passes into the condenser, where it is condensed by cooling

water/air.

The released solution of the generator is sent back to the absorber, where

it is cooled by means of cooling water/air. The refrigerant liquid from the

condenser enters the evaporator and the cycle is repeated.

Types of absorption system:

1. Ammonia absorption system

Refrigerant-Ammonia, Absorbent-water

2. Lithium-bromide absorption system (very popular)

Refrigerant-water, Absorbent, lithium-bromide.

Relative advantage and disadvantages of two systems.

1. Since heat is the operating force of an absorption system so less electric

power is required for this system.

2. Absorption system uses the cheapest, safest and most available

refrigerant, ordinary tap water. Its absorbent is a simple salt.

3. In the absorption system the absence of heavy moving parts practicallyeliminates vibration and reduces the noise level to a minimum. Less

maintenance is required.

4. For the same capacity larger size cooling tower is required for the

absorption system.

5. Crystallization can occur in the absorption system so that special measure

must be taken in the absorption system to avoid crystallization.6. The absorption machine requires more insulation.

Field of application:

1. Where low cost fuel, natural gas is available, the absorption system is

suitable for use.

2. Where waste steam or hot water is available ,the absorption system will

be economical.

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3. Absorption machines may be applied also in conjunction with gas

engines or turbines. It can use the steam or hot water made in a waste

system of boiler/gas engine.

4. Where there is a lack of adequate electric facilities for installation a

compression machine. Because absorption machine use only 2-9% of the

electric power required by compression type machine.

1.3 Air conditioning plant hardware

Evaporator: The evaporator is the component that absorbs the unwanted

heat in the of refrigeration system. Evaporator temperature must always be lower than the temperature of the medium to be cooled.

There are two basic types of evaporators:

1. Dry or direct expansion

2. Flooded.

1. Dry or direct expansion evaporator: It has a coil tubing between the

metering device and the compressor. The dry evaporator uses a

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predetermined amount liquid refrigerant and completely vaporizes the

refrigerant before it reaches the suction line.

These types of evaporator may be sub-divided:

1. Prime surface evaporator (bare type)

2. Plate type: normally found in refrigerators and freezers.

3. Fin-tube type: normally found in window & split type air-

conditioners.

2. Flooded evaporator: A flooded evaporator is completely filled with

liquid refrigerant. In these evaporators secondary refrigerant flows in the

tubes and liquid refrigerant flows in the shell. Since the shell is floodedwith refrigerant, it boils and completely wets the interior walls. The

flooded evaporator system is also known as an indirect system.

Compressors: The compressor takes refrigerant vapour at a low

temperature and raises it to a high temperature and pressure. It pumps

refrigerant throughout the system.

There are three main types of compressors:1. Reciprocating.

2. Centrifugal

3. Rotary

1. Reciprocating compressors: Three types

i) Hermetic compressor (welded): Hermetically sealed, normally

found in window & spit-type units.ii) Semi-hermitic compressor: This is a serviceable hermetic

compressor.

iii) Open-type compressor: In this compressor, one end of the

crankshaft extends through the crankcase and is driven by an

external power source. It may be direct drive or belt drive.

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2. Centrifugal compressor: In the centrifugal compressor, a high-speed

impeller blade rotates within volute (housing). As the blades rotate rapidly theycause centrifugal force to raise the refrigerant gas pressure within the housing.

The centrifugal compressor normally handles large volumes of gas at low

compression ratio.

3. Rotary Compressor: In the rotary compressor, a vane rotates within a

cylinder. A rotary compressor is a positive-displacement compressor. Two types

are in common use.

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i) Rotary sliding vane.

ii) Helical rotary screw compressor : Male and female helical rotors are in

the housing with suction and discharge ports. The male rotor is called lobe and

the female rotor is called grove. The suction port is normally at the top of the

compressor and the discharge port at the bottom. Suction enters the compressor

port to the unmeshed rotors. As the rotor turn and start to mesh, they compress

the suction gas. The volume area decreases thus increasing the vapour pressure.

The helical rotary screw compressor becomes popular in large plants because of

its less power consumption and smooth and quiet operation.

Condensers: It is heat rejection equipment. It transfers heat from the

refrigeration system to a medium that can absorb it. The condensing

medium must always be colder than the refrigerant it is condensing.

There are three types of condenser commonly used:

1. Air-cooled condenser

2. Evaporative condenser 3. Water-cooled condenser.

1. Air-cooled condenser : In which heat is rejected directly to the air. Space

is not needed for piping, cooling towers, water pumps. These types of

condensers are most commonly used in relatively small refrigeration system.

Three types of air-cooled condenser:

(i) Natural draft condenser: Ambient air is the condensing medium.(ii) Forced-air condenser: A fan pushes air through the condenser coil.

(iii) Inducted air condenser: A fan draws or pulls the air over the condenser

coil.

3. Evaporative condenser: In which sprayed coils used to dissipate the

heat to the air by sensible and latent heat transfer. Both air and water are

employed as a condensing medium.

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3. Water-cooled condenser: In which heat is transferred to water. It uses

water as the condensing medium. There are three types water-cooled

condensers.

i) Tube-in-tube or double pipe condenser: A small diameter pipe is

inserted into a bigger diameter pipe. Water flows through the inner tube and the

refrigerant through the annual space between the two tubes. In this system

cleaning is not easy.

ii) Shell-and-coil condenser: It consists of a welded sheet shell containing a

coil of finned tubing in which water flows, the refrigerant being in the shell.

Since the tube bundle is in the form of coil, the waterside of the tube cannot be

brushed but can only be cleaned chemically.

iii) Shell-and-tube condenser: In this condenser refrigerant is in the shell

and water is in the tubes. The water box is bolted to the tubes at each end.

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Depending on the number of baffles inside the unit, water may pass several

times. This type of condenser is easy to clean waterside, it is very popular.

Pumps:

Centrifugal pumps are mostly used with air conditioning and refrigeration

systems. The centrifugal pump is rated on the basis of capacity i.e. volume of

liquid per unit time (gpm), against a head (feet of water) and the energy

required at a given speed.

Pumps are selected from manufacture’s performance curves. Most

standard pumps are designed to operate at maximum efficiency about

midway on the head-capacity curve. Selecting a pump at the maximum

efficiency point or slightly to the left assists in minimizing problems of

noise and vibration. The suction piping at the centrifugal pump must be

designed with care to avoid possible malfunction.

Air handling units: An equipment consists of cooling and/or heating

coil, a blower or fan with electric motor and air cleaning componentsused for the purpose of cooling/heating and distributing supply air to a

room or area. When a duct system is needed in an air conditioning

application, AHU may be used.

The parameters, which influence the selection of an AHU, are air

quantity, static pressure, sound level, available space and the nature of the

load.Fan coil units: The primary components of a fan-coil unit are a fan to

produce a flow of air and a chilled water or direct expansion coil to cool

and dehumidify the air. FCU units are suitable for using in a multi-room

application where load consumption varies independently and as a

function of time.

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to the condenser. Make-up water is supplied to the tower, controlled by a float

valve.

Operation and Maintenance:Good operation and maintenance is only possible if all plants and

machinery are properly installed & commissioned. If the plant room is

very much crowded, leaving little space for the servicing or replacing of

components, the service time increases. There should be i) sufficient

space for cleaning/brushing of the condenser and chiller-water tubes (ii)

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accessibility to clean air-cooled condensers and cooling coils (iii)

sufficient space between the ends of the motor and compressor shaft etc.

Operation:

At the time of operation the following points should be checked &

insured:

Check the power supply (within the rated voltage).

Ensure that guards are provided for all rotating parts.

Check the proper operation of safety controls such as high pressure, low

pressure & oil pressure cut-outs, water flow switches, overload elements of

all motors, the thermostats, etc.

Maintain a record of day-to-day readings of the plant known as log. The log

helps in trouble shooting at a later stage. Some reading are given below.

a) Compressor: Oil level, oil pressure, suction/discharge pressure.

b) Motor: Voltage, current.

c) Condenser: Pressure, Disch. temp, inlet & outlet temp. of water, flow

rate, pressure drop.

d. Cooler: Pressure, suction temp, inlet & outlet temp of water, flow rate,

pressure drop.

e) Pumps (condenser/chilled water): Suction & discharge pressure.

f) Cooling tower: WB approach.

h) AHU: Intel & outlet temp.

Maintenance:All mechanical equipment needs strict maintenance. Proper and timely

periodic check & maintenance can save considerable amount of time,

material & money. The program of regular daily, weekly, monthly checks

and annual maintenance along with checklists shall be made with the help

of manufacturer instruction manual. Preventive maintenance includes the

following:

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Evaporators/Chillers:

Clean air filters regularly.

Clean/wash the evaporator coil periodically.

Clean strainers and filters in the water system regularly.

Brush water tubes in chillers at least once in a year.

Check and rectify oil return problems etc.

Evaporators/Chillers:

Clean air-cooled condensers regularly with compressed air or an air blower.

Clean/descale condenser water tubes periodically (twice in a year).

Clean strainers in water regularly.

Cooling tower:

Drain and clean the cooling tower tank periodically.

Clean cooling tower water strainers regularly.

Check the spray nozzles and headers for proper operation.

Check fan belts for wear and proper tension.Lubrications of fans shaft, pump and motor bearings etc.

Compressor & Motor:

Check oil filter and oil level regularly .

Compressor bearings should be periodically checked for wear.

Check compressor motor mounting for tightness & vibration

Meg. Motor windings annually to check for deterioration of winding.

etc

AHU & Pump-motor:

Clean air filter regularly once in a fortnight.

Check fan belts for wear and proper tension.

lubrication of fan shaft, pump and motor bearings.

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Electrical Controls:

All the safety and operating controls should be checked periodically for

proper operation.

1.4 Vibration & Noise

Source of vibration & noise:

In air-conditioning system air handling, pump-motor, blower,

compressor produce noise & vibration.

Motors produce airborne sound and physical vibration. The undesirable

manifestation of sound and vibration is termed noise. Airborne noise is produced by all the vibrating parts of the motor. The initial sources are

magnetic, mechanical and windage.

Magnetic noise is produced by magnetic forces (flux) in the air gap and

other parts of a magnetic circuit. Mechanical noise may result from

misalignment, disrepair, unbalance or bearing disorder.

Windage noise is produced by ventilation air through the motor together with propulsory elements.

Improper coupling between the motor and its support may transmit

unwanted vibration & noise to building structure.

Duct & piping system unless adequately designed, may act as a

significant sound source and will transmit noise through out the building.

Methods of elimination of vibration and noise:

The foundation of the rotating machine should be heavy to reduce vibration

and should be properly aligned & level.

Insulators should be used to absorb the vibrations produced by AHU as well

as other rotating machinery.

Disorder bearings of rotating machinery should be replaced timely and

bearings should be well-lubricated.

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Canvas tape or asbestos cloth connectors should be used for all duct

connection to fans and air-conditioners to minimize sound transmission.

Insulating/sound absorbing material should also be used to guard against

noise.

Sound traps, duct liner, vibration isolators and duct stiffeners might be

required to damper the generated noise and vibration in certain critical areas.

Relevant BNBC/93 code:

3.3.3.4 Noise Control:

a) Air Ducts: Air ducts shall be so designed and installed to avoid any

transmission of noise and vibration which may be picked up by the duct system

from equipment room or a adjoining rooms. Duct system shall not allow cross

talk or noise transfer from one occupied space to another.

Duct system shall be appropriately designed, constructed and installed to obtain

adequate attention of noise required to maintain recommended noise level in the

air-conditioned space.

Duct construction and installation shall be such that drumming effect of duct

walls and noise transmission through the duct wall can be minimized to

approved level.

b) Plenum Chamber: If required, properly designed plenum chamber, lined

with approved sound absorbed material, and or sound attenuators shall be used

for attenuation of noise.c) Flow Control Devices: Air dampers and other flow control devices shall

be so selected that noise generation do not exceed approved levels.

d) Air terminals: Air terminals shall be selected for the approved noise

generation characteristics.

e) Piping: Velocity of fluids in piping shall be so selected that noise

generation do not exceed approved levels.

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1.5 Refrigerants

A refrigerant is a fluid in a refrigeration system that picks up heat byevaporating at a low temperature and pressure and gives up heat by condensing

at a higher temperature and pressure.

Desirable Characteristics of refrigerants:

Low-boiling temperature.

High latent heat of vaporization.

Non-flammable, non-explosive, non-toxic.Chemically stable.

Non-corrosive.

Moderate working pressures.

simple detection and location of leak

Non injurious to lubricating oil.

Low freezing temperature.

High critical temperature.

Low cost.

Moderate specific volume of vapour.

Types of refrigerants:

1. CFC(Chlorofluorocarbons): CFC refrigerants contain chlorine, fluorine

and carbon. They reach the ozone layer and deplete it. Most used CFC

refrigerants: R12, R22, R113, R114, R500 and R502

2. HCFC(hydrochlorofluorocarbons): HCFC refrigerants contain

hydrogen, chlorine, fluorine and carbon. HCFC-123 is substitute for R11

and HCFC-124 is possible substitute for CFC-114.

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3. HFC (hydrofluorocarbons): Which contains hydrogen, fluorine, and

carbon.

All fluorocarbon-based refrigerants are heavier than air. It is believed that

they harm the ozone layer less than CFCs.

Ozone layer depletion and green house effect due to CFCs:

Approximately 20 to 30 miles above sea level is the ozone layer, part of

the earth’s atmosphere. Ozone layer absorbs ultraviolet rays from the sun

and shields the earth from much of the damage caused by ultraviolet rays.

But CFC refrigerants reach the ozone layer and deplete it through a

chemical reaction. Ozone depletion allows ultraviolet rays to enter the

earth’s atmosphere and harm humans, animals and plant life. Ultraviolet

rays also raise the heat of earth’s atmosphere like as green house.

Safe handling of refrigerants:

Refrigerant cylinders should never be heated and cylinders are under

pressure and should be treated with respect.

Non-refillable cylinder should never be refilled.

Do not drop, tamper, or abuse cylinders.

Do not spill liquid refrigerant on the skin.

Gloves, protective clothing, and goggles should be used whenever handling

refrigerants.

Charging refrigerant:

There are two methods for charging refrigeration systems.

i.) Vapour charging

ii.) Liquid charging

i) Vapour charging: Small systems are usually vapour charged

through the gauge port of the compressor suction service valve.

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ii) Liquid charging: liquid refrigerant is introduced into the system

through the charging port on the downstream side of main liquid

line.

1.6 Ventilation

Requirements :

Introduction of outdoor air for ventilation of conditioned spaces isnecessary to dilute the odors given off by people, smoking and other

internal air contaminants.

Outdoor air normally has a different heat content than the air within the

conditioned space and therefore ventilation air impose a load on the air

conditioning equipment.

Types of ventilation:

i. Natural ventilation

ii. Mechanical ventilation (by mechanical means)

The amount of ventilation air requirement varies primarily with the total

number of people, ceiling height and intensity of smoking.

- 7.5 cfm air per person is recommended for dilution of body odors.

- Minimum 15 to 25 cfm per person when people smoke.

Air change requirements in buildings and establishment.

Ventilation in certain area such as operating room, autopsy room,

delivery room, intensive care unit etc. is very critical. In these area

ventilation system is designed so that it mix and change room air at a

predetermined rate to facilitate removal of order and rodon gas, low level

of airborne bacterial contamination & concentration anesthetic gases.

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Required air charge requirements are given below as per BNBC/93 code:

3.7.4.2(Table 8.3.6)

Autopsy room 12 air changes/hour.

Delivery rooms, trauma room 15 air changes/hour.

Laboratories room 6 air changes /hour

Operating rooms 20 air changes /hour.

Intensive cave rooms 6 air charges/hour.

1.7 Water heater, Space heater and Geysers, control of temperature,

air and motor flow in these systems.

Space-heater:

Electric heaters that are used to heat air space in the room or area are

called space heaters. They are manufactured in various sizes and types to

suit different conditions of service and heat requirement. Irrespective of

their construction and size, they all work on the electrical resistance

principal; that is, a length of resistance wire becomes heated when an

electric current passes through it.

There are several types of space heaters:

1. Bowl-type heater (radiant)

2. Convection type heater

3. Immersion type heater

4. Forced draft heater.

Bowl type heater has obtained its name from the bowl-like shape of its

metallic reflector. The reflector bowl radiates heat in a cone-shaped wide

beam.

The Convection type heater consists of performed sheet metal cases

through which air can circulates over the heating element surface. The

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warmed air, through convection, is caused to rise, thereby providing

circulation of warm air in the room. The heating elements consists of

resistance wire wound on cylindrical insulators.

Immersion heaters , often called electric steam radiator, are so designed

that the heating units can be placed directly in the water to be heated.

Immersion heaters may be equipped with thermostats for automatic

temperature control.

Forced draft heater consists of one or more heating elements and an

electric fan, which blows the heated air through the heating units and

circulates it is a given area. This type heaters are available with or without thermostats for room temperature control.

Water Heaters/ Geysers:

There are two types of water heaters:

i) Electric water heater.

ii) Gas fired water heater.

i) Electric water heater: An automatic electric water heater consists of ametal water-storage tank that is heavily insulated to prevent the escape of heat.

One or two electric heating elements, with the necessary thermostatic and safety

controls, are mounted inside the storage tank. The heating coils are shielded

from direct contact with the water with a metal watertight enclosure. The

heating units are immersed in water. All tank seams are welded and are usually

tested with a hydrostatic pressure of approx. 300 psi. The tank capacity mayvary and is directly dependent on the hot water demand.

The heating element is equipped thermostats to control water temperature

automatically. Most thermostats used for water heaters have a range of from

100 0F to 200 0F and they are usually set at the factory to deliver water a constant

temperature at the tank outlet.

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ii) Gas Water heater: Gas water heaters are those in which the hot water

tank, the gas burner, the combustion chamber and the necessary insulation are

combined in a single unit with provision for an automatic supply of hot water.

Water tank sizes very, depending on their requirement. In this type of heater, the

heat from the gas flame is transmitted to the water by direct conduction through

the tank bottom and flue surfaces. Some heaters have multiple central flues,

while in other designs the hot exhaust gasses pass between the outer surfaces of

the tank and the insulating jacket. The gas waters are usually equipped with

thermostat, thermocouple, pressure-relief valves etc. Thermocouple is used to

ignite the burner and pressure relief valves are used to relieve excessive

pressure in the heating system. Gas water heater is suitable & economical for

using in relatively large water consumption. Initial investment is higher.

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